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An officer is placed on leave, United's CEO is under fire, and customers are outraged after a man was violently removed from an overbooked flight.

"If they had just tried some diplomacy, none of this had to take place," passenger John Klaassen said Tuesday.

By now, most everyone's seen the cell phone footage: Security officers dragging the man down the plane's aisle by the arms and legs while other passengers shout in protest. The man has been identified as Vietnamese-American Dr. David Dao.

What prompted the backlash is how the airline and officers handled the situation -- both aboard United Flight 3411 and in the company's initial response Monday. On Tuesday afternoon, CEO Oscar Munoz offered a full apology, calling the incident "truly horrific" and pledging a "thorough review" by April 30.

"I continue to be disturbed by what happened on this flight," he said in a statement, "and I deeply apologize to the customer forcibly removed and to all the customers aboard. No one should ever be mistreated this way."

The man who ended up bloodied and screaming Sunday night had initially agreed to get off the plane, passenger Jayse Anspach said.

"Him and his wife, they volunteered initially," Anspach said. "But once they found out that the next flight wasn't until (Monday) at 2:30 p.m., he said, 'I can't do that. I gotta be at work.' So he sat back down."

The harder the officers tried to get the man to leave, the harder the man insisted he stay.

"He was very emphatic: 'I can't be late. I'm a doctor. I've got to be there tomorrow,' " Anspach recalled.

His pleas didn't work. Moments later, the man was getting dragged down the aisle. At one point, passengers say, the man hits his head on an armrest. Video shows blood starts streaming from his mouth.

During the ordeal, the man claimed he was being profiled for being Chinese, passenger Tyler Bridges said.

On Tuesday afternoon, Dao's lawyers said he was being treated at a Chicago hospital.

"The family of Dr. Dao wants the world to know that they are very appreciative of the outpouring of prayers, concern and support they have received," Chicago attorney Stephen L. Golan said in a statement. The family won't speak with the media until Dao is released from the hospital, according to the statement.

Overbooking is legal, and most airlines do it in anticipation of no-shows, the US Department of Transportation said. If no one volunteers to get off, the airline can select passengers for removal based on criteria such as check-in time or the cost of a ticket, according to the department's Fly-Rights.

On the United flight, no one volunteered to leave, so the company was forced into an "involuntary de-boarding situation," airline spokesman Charlie Hobart said.

United employees explained the situation to the man several times, Hobart said. When he refused, they followed Department of Transportation protocol and called local law enforcement to forcibly remove him from the plane. At least one of those responding officers is now under investigation.

Security officer put on leave

Bridges said two officers tried to calmly talk the man out of his seat before a third approached him aggressively. That officer told him he had to get off the plane, and when he resisted, the officer grabbed him out of his seat and carried him out with the other officers.

The Chicago Department of Aviation, said the incident "was not in accordance with our standard operating procedure, and the actions of the aviation security officer are obviously not condoned by the Department."

That officer has been placed on leave pending an investigation, the department of aviation said.

CEO gives no apology, praises employees

In an internal memo, CEO Oscar Munoz defended his employees, saying the passenger kept trying to resist after he was removed -- and ran back into the plane.

"Our employees followed established procedures for dealing with situations like this," Munoz wrote. "While I deeply regret this situation arose, I also emphatically stand behind all of you, and I want to commend you for continuing to go above and beyond to ensure we fly right.

"I do, however, believe there are lessons we can learn from this experience, and we are taking a close look at the circumstances surrounding this incident."

"The apology by the CEO was, at best, lukewarm or, at worst, trying to dismiss the incident," Younger said. "The CEO should make a better, more heartfelt, more meaningful and more personal apology."

But passenger Bridges said he holds United responsible for the fiasco.

"I think United messed this up on the front end," he said.

"It shouldn't have gotten to the point where there's a man on the plane or four people on the plane that have to be removed after they've already taken their seat. If they were overbooked, they should have only let people on the plane that were going to be able to leave on the plane."